LR Question 19 Explanation
QUESTION TEXT: Birds need so much food energy to maintain their body…
QUESTION TYPE: Necessary Assumption
CONCLUSION: Seed eating birds must spend more time eating than nectar eating birds that have the same energy requirements.
REASONING: A given amount of nectar provides more energy than an equal amount of seeds.
ANALYSIS: This has told us how much energy each type of food has. But hasn’t told us how long it takes to eat each type of food.
___________
- All the argument has to assume is that occasionally birds of different types have the same energy requirements. That’s how they can make the comparison.
- This isn’t necessary. Even if a nectar eating bird eats a few seeds it will still mostly eat nectar.
- CORRECT. If the nectar eating bird takes longer to eat the nectar than the seed-eating bird, then the nectar eating bird might have to spend more time eating. Total eating time depends both on how much energy the food has and how long it takes to eat it.
- Body temperature doesn’t matter as long as each type of bird has the same energy requirements. Birds just have to eat enough to maintain their body temperatures (whatever temperature that happens to be for each bird.)
- It doesn’t matter what influences a bird’s overall energy needs. The stimulus is comparing two birds that have the same energy requirements.
More Resources for Necessary Assumption Questions
- Negations Article: Learn about negations on the LSAT.
- Conditional Reasoning Article: Learn about conditional statements.
- Negations Drill: Practice your negation skills.
- LR Diagrams Guide: Learn how to draw LR diagrams.
- Intro to Conditional Reasoning: Learn conditional reasoning basics.
- Intro Course lesson: This intro course lesson covers Necessary Assumption questions.
- Mastery Seminar lesson: This LR Mastery seminar lesson covers necessary assumption questions.
For the sake of completeness, it might be interesting to note that, despite being the only feasible answer choice, C is not, strictly speaking, a necessary assumption.
Here is a scenario which directly contradicts C, although it is consistent with all the premises and the conclusion:
Let’s say both the seed-eating and the nectar-eating birds need to consume 100 cal worth of food each over the same period (“same overall energy requirement”), and nectar(4 cal/g) has four times the energy content of seeds(1 cal/g) (“nectar provides more energy than does the same amount of seeds”).
Good catch! Yes, that’s correct. This is a good illustration of the instructions telling us to pick the best answer. C is clearly correct, but even the argument’s author might dispute that they assumed two equivalent quantities of food took exactly the same amount of time.
autocorrect in AC C for Preptest 30, LR 2, Q19
CORRECT. If the nectar eating birds takes longer to eat the nectar THAN the seed-eating bird, then the nectar eating bird might have to spend more time eating. Total eating time depends both on how much energy the food has and how long it takes to eat it.
Yes, that’s correct, thanks for catching these typos! The page has been updated.